A number of psychoactive agents adversely affect brain development. However, underlying molecular mechanisms remain to due, in part, to the complexity and inaccessibility of the brain, particularly in developing animals. We, however, are now able to approach questions of molecular mechanisms governing toxicity in the central nervous system (CNS). We have succeeded in growing the brain nonadrenergic nucleus locus coeruleus in an accessible tissue culture system for prolonged periods. Electrophysiological studies indicate that the locus is responsive to a variety of psychoactive substances, including caffeine, ethanol, amphetamines and tricyclic antidepressants. Moreover, the locus exhibits sensitive and specific phenotypic characters by which ontogeny and toxicity may be monitored at defined molecular loci. In the proposed work, we will evaluate the influence of caffeine, ethanol,locus amphetamines and the tricyclic antidepressant, desmethylimipramine, on ontogeny. Effects of these agents will be assessed by monitoring the noradrenergic traits, tyrosine hydroxylase, dopamine-8-hydroxylase and the specific uptake of norepinephrine, sensitive and specific markers of locus function Specific antagonists will be used to define receptor sites involved in any observed drug action. In addition, agents will be tested on locus cells of varying maturities and critical developmental periods will be defined. Finally, mechanisms underlying ontogeny of drug dependency and tolerance will begin to be evaluated by examining coeruleal traits after prolonged exposure to the psychoactive agents. These experiments promise to identify the molecular loci of action of drugs of abuse in the brain.